EM thin section analyses of infected cells and of particles in iodixanol gradient fractions. A. HHV-6A infected cells at 3 dpi. Indicated are viral nucleocapsids (thin arrows) in cell nuclei and virions released into the extracellular milieu (thick arrow and insert). The bar is 1000 nm. B and C. Material in gradient fractions 11–15. Note the intact and morphologically preserved HHV-6A particles in material from HHV-6A-infected cells (B) and their absence in samples from mock-infected cells (C). The bars are 500 nm.